Here in Calgary, in May and June have the longest daytime. It should be the best time for plants growing. But the temperature is too low especially at night. Many kind of veggie don’t grow in these two months.So I am considering buying a Twin wall polycarbonate panel greenhouse. However, once I have a greenhouse, my issue becoming the temp will too high in the sunny and warm days, with two vents open for an 8x12’greenhouse, I am wondering how high the temperature will reach in July in Calgary? I beg some advice from the people how have a greenhouse, and tell me how are you guys dealing with this issue? Thanks

Heaters, vents, and fans are your allies in temperature control in a Greenhouse.

Vents and fans help to cool the greenhouse. On a sunny day, even at 20°F below zero, greenhouse air can heat up well beyond healthful levels. In a freestanding unit, hot air must have a way to exit, and cool air a way to enter. Passive vents allow for this sort of movement, as do thermostatically controlled exhaust fans and intake vents. Manually operated vents are relatively inexpensive, but you’ll need to check them at least twice a day, and open or close them as necessary. Automatic ventilation systems are more costly, but they save time and reduce the chances of excessive cooling or heating.

Adjust air temperature in the greenhouse according to the level of light. In general, summer crops grow best at temperatures of about 75° to 85°F in the daytime and 60° to 75°F at night. On cloudy days, these temperature ranges should be somewhat lower, since the plant is not manufacturing as many sugars as usual.

Winter air temperatures can go as low as 45°F at night without damaging most leafy green crops and shouldn’t go much above 65° to 70°F during the day. Spring seedlings vary in their temperature preferences. Cool-weather crops, such as broccoli and lettuce, grow most vigorously at 50°F nights and 60° to 65°F days, while warm-weather plants such as tomatoes and squash require nights at a minimum of 55°F and days of at least 65°F but no higher than 80°F.